In Croft Manor, Lara found a old book of her father, Richard Croft. Lara open it and discover in a page, it says:

Hello, Lara, my darling daughter. I will tell you a beautiful story. In the ancient years, in the villages of Thailand, the people loved an ancient artefact called the Crystal Amulet. Their believe the amulet brings happiness and good things for the villages. It was sacred, and the gods keep it inside of a temple. But the time runs, and an earthquake killed all the civilization, and it left ruins. But the Crystal Amulet still in the sacred room of the temple. And now, various people want it, like Von Croy. The amulet is so precious and cost billions of gold! Don't let that mercenaries pick it! Run Lara, catch the amulet!